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Harvard Forest Symposium Abstract 2013

  • Title: Effects of Soil Warming on Carbon and Nitrogen Cycling
  • Primary Author: William Werner (Marine Biological Laboratory)
  • Additional Authors: Chelsea Baldino (Marine Biological Laboratory); Frank Bowles (Research Designs); Sarah Butler (Marine Biological Laboratory); Jerry Melillo (Marine Biological Laboratory); Lindsay Scott (Marine Biological Laboratory)
  • Abstract:

    One consequence of a warmer world will be warmer soils. This has the potential to alter plant and soil processes in temperate forests that affect their carbon storage capacity, and the effects could be large enough to impact both the global carbon cycle and the course of future climate change. Over the last ten years, we have assessed the consequences of soil warming on carbon storage, nitrogen cycling, and tree growth in a large (30 x 30 m) plot at Harvard Forest by warming the soil to 5ºC above the temperature of an adjacent control plot. This warming has accelerated soil organic matter decay, increasing the CO2 flux from the soil to the atmosphere at a mean annual rate of 1.54 Mg C ha-1. Warming has also increased carbon sequestration in plant biomass by 1.04 Mg C ha-1. Over the course of the experiment, the additional carbon sequestration due to accelerated tree growth in the warmed plots has compensated for about two thirds of the additional carbon loss from the soil.

    Soil warming has accelerated nitrogen mineralization, increasing nitrogen availability at a mean annual rate of 31.8 kg N ha-1. We attribute the increases in plant carbon storage in the heated plot primarily to the warming-induced increases in nitrogen availability.

    The nitrogen chemistry of green leaves has changed with increased nitrogen availability and this change is consistent with our observation of increased plant carbon storage. Leaf N concentrations are higher in the heated plot than in the control, with the most consistent increases being in red maples. Additionally, we have also observed an enrichment of 15N in canopy leaves across all species, which suggests that warming is facilitating the release of nitrogen from more recalcitrant forms of soil organic matter.

    Although we think that most of the increased carbon storage in the trees is related to the warming-induced acceleration of the nitrogen cycle, we have observed a lengthening of the growing season with warming. In the spring, trees in the heated plot are breaking bud 4-7 days early.

    This study underscores the importance of considering the links between the carbon and nitrogen cycles in projecting the effects of a key component of climate change, warming, on the carbon balance in the forests of New England.

  • Research Category: Forest-Atmosphere Exchange
    Large Experiments and Permanent Plot Studies
    Soil Carbon and Nitrogen Dynamics

  • Figures:
  • EcosystemCarbonFlux.png
    NitrogenMinerialization.png